SET08112

From Progzoo
Revision as of 23:03, 26 January 2011 by Andr3w (Talk | contribs) (Problem 3 - Who's missing?)

Jump to: navigation, search

SET08112 ArrayList Interface Tutorial

In this tutorial you will use the ArrayList and the HashMap or TreeMap to solve some common problems. You will use methods such as:

  • java.util.Collections.sort
  • add
  • get

Problem 1 - Sort a List

The file from http://www.dcs.napier.ac.uk/~cs66/SET08112/tut2/students.txt contains a list of students:

ADAMS, ROBERT
HASTIE, MARTIN
OTHIENO, JUDITH
ANDERSON, ROSS
...

Create a programme SortStudents.java that reads in this file and outputs the students in Alphabetical order.

  • You can use an ArrayList to hold the students.
  • ArrayList<String> names = new ArrayList<String>();
  • You can use java.util.Collections.sort to sort the ArrayList


[Font] [Default] [Show] [Resize] [History] [Profile]

Problem 2 - List Routes

The file year1.txt contains a list of all students in year one. Each line contains the name of the student and the name of the route (programme) they follow separated by a tab.

Brando, Marlon 	BSC (HONS) DIGITAL MEDIA F/T
Bridges, Jeff 	BSC (HONS) INTERACTIVE MEDIA DESIGN F/T
Brody, Adrien 	BENG (HONS) COMPUTER SECURITY AND FORENSICS F/T

Write a program to read in this file and output a list of routes with no duplicates. You can use a program very similar to the one above – but this time:

  • Use line.split("\t") to get the route
  • Use name.contains(st[1]) to add the route only if it is not already in the ArrayList
  • You do not need to sort before output



[Font] [Default] [Show] [Resize] [History] [Profile]

Problem 3 - Who's missing?

The file present.txt contains those students from students.txt who attended a particular tutorial. We want a list of all those students who were not present.

Brody, Adrien
Irons, Jeremy
Spacek, Sissy

How to do this…

  • Create an array list called present
  • Open the file present.txt and add every line to the ArrayList present
  • Open the file student.txt
  • For each line in the file – if that student is not in present print the name.
if (!present.contains(line)) System.out.println(line);


[Font] [Default] [Show] [Resize] [History] [Profile]

Problem 4 - Count Routes

Use the file year1.txt to print a list of all the routes in alphabetical order. We also want a count of how many students are in each route.

BENG (HONS) COMPUTER NETWORKS AND DISTRIBUTED SYSTEMS F/T	10
BENG (HONS) COMPUTER SECURITY AND FORENSICS F/T	28
BENG (HONS) COMPUTING F/T	22
BENG (HONS) EMBEDDED COMPUTER SYSTEMS F/T	1
...

How to do this:

  • See the section “Use Map to aggregate” from the lecture
  • You can use two passes to process get the answer.
    • On the first pass run over the list and put the value 0 against every route you encounter.
    • On the second pass use put to add 1 to each route you encounter.
  • It is better to use a single pass:
    • For each route if the key exists then +1 of the value, if the key does not exist then put 1.


[Font] [Default] [Show] [Resize] [History] [Profile]